Mobile phones of today have evolved from merely being phones to full-fledged computing, sensing, and communication devices. These features of mobile phones coupled with their ubiquity have paved a way for an exciting new paradigm for accomplishing large-scale sensing, i.e. participatory sensing. Participatory sensing is a concept of communities (or other groups of people) contributing sensory information to form a body of knowledge. One key idea of participatory sensing is to empower ordinary persons to collect and share sensed data from surrounding environments using their mobile devices. For example, cameras on mobile phones can be used as video and/or image sensors; embedded Global Positioning System (GPS) receivers on mobile phones can provide location information.